Console Power Supply help

[ROSA]

Hello,

I have an old Soundcraft power supply that I would like to clean up for use with a 500 series rack. I've been able to lower the output voltage of the LM317 and LM337 from +-17v to +-16v by replacing one of the resistor with a variable trim. Phantom power is also marking 48v after cleaning and adjusting the trim pot.

The question I have is if there are other small capacitors I could add to the regulators to clean the dc signal up. Each regulator already has a .1 capacitor connected from the input to ground.

Thanks,
ROsa

 

[user 130681]

There is no need for extra capacitors, the regulators will take care of any noise.

 

[ROSA]

thanks

 

[chilidawg]

If the power supply is at least or more than 10 years old, recommended you replace the electrolytic caps at the input and the output, because they will go bad soon.

Brown sleeve Nippon/United Chemicon KY electrolytic cap is my personal favorite when recapping power supplies because it has a smaller diameter than other brands for the same capacitance value and voltage rating, so easier to drop in when space is tight.

Just make sure you measure each capacitance first and it should be at least within 10% tolerance from the capacitance value printed on the sleeve before you solder them in, because sometimes a newly bought and perfectly good-looking cap can be a bad cap.

 

[ROSA]

Yes, was planning to do that and have ordered the new caps. Hadn’t thought of measuring them before installing though, so thanks for that thought.

 

[Whoops]

The question I have is if there are other small capacitors I could add to the regulators to clean the dc signal up. Each regulator already has a .1 capacitor connected from the input to ground.

I don't know the complete circuit of your PSU,
but in terms of filtering compare it to the JLM PSU's circuit and if you're missing something add it to your PSU. here is the schematic:

http://www.jlmaudio.com/ACDCVer2sch.pdf
The JLM PSU is a well proven great and very clean PSU


How many modules/slots will your 500 series rack have?
LM317 and LM337 are rated at max 1,5 Amps, I would use that PSU in a 5 slots rack but I would not use it an 8 slot or 10 slots rack, for that I would personally want a PSU that woulbe be able to deliver around 3A.

 

[ROSA]

I plan to use it with a 6 slot rack, but don’t have any modules yet, so I’ll watch out for current consumption . Thanks for the schematics. Would anyone know what diodes d11 and d12 are in the circuit for?

 

[Whoops]

Would anyone know what diodes d11 and d12 are in the circuit for?

Input and output short protection if I remember correctly, are there to protected the LM317 regulator

 

[Newmarket]

Would anyone know what diodes d11 and d12 are in the circuit for?

They protect against discharge from a) the output capacitance (eg if the input is shorted) and b) the ADJ capacitor (eg output shorted).
Basically the diodes provide a path for the discharge current so the regulator output doesn't get the hit.

see attachment from Data Sheet.

 

[ROSA]

Thanks